The present invention generally relates to wire fabrics and structures. More particularly, this invention relates to tire beads and their methods of manufacture.
A tire bead is that part of a tire which anchors the tire onto a wheel""s rim. It is essentially an annular tensile member or inextensible hoop. Every tire has two such beads which are located within the rubber or elastomeric matrix which makes up the radially inner-most circumference on each side of the tire.
In the usual procedure for manufacturing tire beads, the ends of individual wires, the exteriors of which are often rubber coated, are fed into a tire bead making machine. Machines of this type are old and well known in the tire building art.
Typical bead-making machines of this type are disclosed in U.S. Pat. Nos. 1,913,336, 2,902,083 and 5,385,621. These machines comprise a rotating drum about which the bead wire is wrapped a predetermined number of turns, dependent upon the strength and/or cross-sectional area of the tire bead desired. Standard equipment on such machines includes the means for automatically introducing the leading end of the wire into a gripper on the drum, intermittently operated means for rotating the drum, a stacking device which moves the incoming wire so as to control and build-up the cross-sectional shape of the resulting tire bead, and a knife to sever the incoming wire at the end of each building cycle. During the pause in the rotation of the drum, the finished tire bead is ejected laterally from the drum.
One deficiency of conventional tire bead making machines is the problem associated with how to deal with the cut ends of the resulting tire bead. The springback nature of the wire ends can result in their coming loose and causing wire misalignments which can result in an unacceptable number of manufacturing interruptions in order to restring and realign the wires. At present, string wrapping or stapling the cut end wire portion of a bead is the only way to control end wire movement during the curing process. For example, U.S. Pat. No. 4,938,437 provides a variety of staple-like and string wrapping methods for holding the bead assembly together and constraining the cut wire end.
Thus, despite the prior art, there still exists a need for more efficient tire bead manufacturing processes that can resolve the above-described difficulties.
It is an object of the present invention to provide a more efficient tire bead manufacturing process as defined in one or more of the appended claims and as such, having the capability of accomplishing one or more of the following subsidiary objects.
An object of the present invention is to provide a method of constructing a tire bead by wrapping the final turn of the bead wire so that the cut end is constrained between the two previous wraps of the wire and does not require string wrap or stapling.
Another object of the present invention is provide a new and improved type of tire bead where the wire cut end is constrained to preserve the integrity of the bead core geometry during its removal from the bead making machine and throughout the tire manufacturing process.
Other objects and advantages of this invention will become readily apparent as the invention is better understood by reference to the accompanying drawings and the detailed description that follows.
The present invention is generally directed to satisfying the needs set forth above and the problems identified with prior tire bead manufacturing processes. Prior problems, associated with the springback of the cut wire end and associated interruptions in the bead core manufacturing process and the quality of finished tires are resolved by the present invention.
In accordance with one embodiment of the present invention, the foregoing need can be satisfied by providing a method of making a tire bead core characterized by the steps of winding a length of wire into a coil with at least one radially outermost layer having a side-by-side relationship where each successive winding of the wire is placed adjacent to the previous winding except for the final two windings where the next to last winding is placed with a uniform gap relative to the previous winding and where the final winding and its cut end cross over the next to last winding and are pressed into the gap and are thus constrained by the previous two windings of the bead wire.
Preferably the last winding crosses over the next to last winding at a position of from 210 to 270 degrees rotation of the last windings. The underlying windings of the bead wire can wound in side-by-side relation and in any number of successive superimposed layers of predetermined widths to provide a tire bead core of any cross sectional area and shape including hexagonal. The bead wire is typically coated with an elastomeric material, such as green rubber, prior to winding the bead core.